The present invention relates to a magnetic head for use in magnetic recording and reproducing of information in and from a magnetic recording medium.
In recent years, there is an increasing demand for higher recording density in magnetic recording. To cope with this demand, it is necessary to develop a magnetic recording medium having a greater coercive force, as well as a magnetic recording head having improved performance. For instance, a magnetic head is demanded which has a high level of saturation magnetic flux density and magnetic permeability, in order to fully utilize the merits of magnetic recording mediums having high coercive force. For this reason, conventionally used ferrite materials are being replaced by crystalline magnetic alloys such as Ni-Fe and Fe-Al-Si alloys and amorphous magnetic alloys such as Co-Nb-Zr or Co-Ta-Zr.
Track width and gap length of the magnetic head also are reduced as a result of an increase in the recording density, requiring a higher precision of machining. The transmission rate is also increased to improve the recording and reproducing characteristics at high frequency. These requirements are met by magnetic heads having multilayered structures. Under these circumstances, techniques for forming thin films such as sputtering, vacuum evaporation and plating, as well as processing technique such as a lithographic technique, are becoming popular and are used in place of conventional machining of bulk materials. Thin-film type magnetic heads produced by these techniques are becoming popular.
In order to make full use of the characteristics of the high frequency region, attempts are extensively made to control the magnetic anisotropy of magnetic films in the magnetic path of the magnetic head. It is known that the magnetic permeability of a magnetic film in a high-frequency region is low in the direction of easy magnetization and high in the direction of difficult magnetization. This is because the magnetization process in the direction of easy magnetization mainly relies upon the movement of magnetic domain walls, while the magnetization process in the direction of hard magnetization relies mainly upon rotation magnetization.
Two methods are available for imparting a magnetic anisotropy to a magnetic film:namely, to apply a magnetic field during forming of the magnetic film and to heat-treat the magnetic film in a magnetic field. By using such methods, it is possible to obtain a magnetic film in which the axes of easy magnetization are aligned in the same direction as the direction of the applied magnetic field. In the case of a thin film, however, it is difficult to set the axes of easy magnetization in the direction of thickness of the film. Usually, therefore, the axes of easy magnetization extend in the film. It is known that the performance of a magnetic head is improved when the magnetic anisotropy is imparted to the magnetic film in the direction of hard magnetization to provide the development of high magnetic permeability in the direction of the magnetic path.
This type of thin-film magnetic head is used for example, in magnetic disk devices for computers as disclosed, for example, in IEEE Transaction on Magnetics, MAG-7, 146, 1971.
FIGS. 14(a) and 14(b) show an example of the thin-film type magnetic head, in a sectional view and in a plan view, respectively. The magnetic head has a substrate 1, a lower magnetic film 2 formed on the substrate, an insulating film on the lower magnetic film 2, a coil 3 on the insulating film, and an upper magnetic film 4 on the coil 3, thus forming a magnetic path. Numeral 5 denotes a surface facing the recording medium, while 6 represents a track width. The magnetic path is formed such that the direction of hard magnetization coincides with the direction to the recording medium. Therefore, the direction 7 of easy magnetization coincides with the direction of the track width which extends in the film plane, whereby a high magnetic permeability is obtained in the direction of the magnetic path.
In general, however, ring-type magnetic heads such as those used in VTRs have complicated configurations, so that it is not easy to align the whole magnetic path in the direction of high magnetic permeability.
FIG. 15 shows a known ring-type magnetic head used in VTRs, as disclosed in INTER MAG CONFERENCE, April, 14-17, 1987.
This magnetic head has a protective substrate 1, a plurality of layers of magnetic film 2 and a protective substrate 1'. This multi-layerd structure is divided into core halves 8 and 8' and, after formation of a coil-winding window 9, these two parts are joined together through a gap material 10. In this case, the track width 6 is in the direction of thickness of the magnetic film. In this ring-type magnetic head, the magnetic path is formed so as to surround the coil window 9. When the principle of the thin-film magnetic head shown in FIG. 14 is applied to the ring-type magnetic head, it is understood that the magnetic anisotropy should be imparted to this ring-type magnetic head such that the direction of easy magnetization exists in the thicknesswise direction of the magnetic film, i.e., the direction of the track width which direction is perpendicular to the direction of the magnetic path. In the ring-type magnetic head shown in FIG. 15, however, it is difficult to set the direction of easy magnetization in the thicknesswise direction of the film, because of the influence on the demagnetizing field, especially when the film thickness is reduced to, for example, 10 .mu.m or less for the purpose of enhancing the track density.
A similar effect can be obtained when axes of easy magnetization are provided in a radial direction with respect to a ring-type core. From a view point of mass-production, however, it is extremely difficult to control all of the axes of easy magnetization along and perpendicularly to the magnetic path.
In the magnetic circuit including the magnetic head, the characteristics of the magnetic head are largely influenced by the magnetic resistance occurring in a region which is in the vicinity of the operation gap adjacent the head face opposing the recording medium. It is understood that an appreciable improvement in the characteristics is attainable by aligning the direction of easy magnetization in the above-mentioned region with the direction of running of the magnetic recording medium. In this case, however, the portion of the magnetic path behind the above-mentioned region becomes parallel to the direction of easy magnetization so that satisfactory head chracteristics cannot be obtained. Further, the thickness of the magnetic film is reduced in the case of heads having small track widths of 10 .mu.m or less. Therefore, in the magnetic head of the type shown in FIG. 15 having a comparatively large length of the magnetic path, the magnetic resistance of the magnetic path is generally high, which makes it impossible to obtain sufficiently high levels of reproducing output.
As has been explained, the prior art magnetic heads have the problem that the magnetic recording/reproducing characteristics are not fully improved when the track width is reduced. In particular, in the ring-type head in which the track width appears in the direction of the film thickness, the magnetic recording and reproducing characteristics are impaired and fluctuated due to difficulty encountered in setting the direction of easy magnetization perpendicular to the magnetic path.